diff --git a/shapes/Intersect.cc b/shapes/Intersect.cc
index a4c421e..2546c1c 100644
--- a/shapes/Intersect.cc
+++ b/shapes/Intersect.cc
@@ -33,6 +33,8 @@ Shape::IntersectionList Intersect::intersect(refptr<Shape> _this, const Ray & ra
 {
     Ray ray_inv = m_inverse.transform_ray(ray);
     IntersectionList res1 = m_shape1->intersect(m_shape1, ray_inv);
+    if (res1.size() == 0)           /* optimization */
+        return res1;
     IntersectionList res2 = m_shape2->intersect(m_shape2, ray_inv);
     BoolIntersectionList merged(res1, res2, ray_inv.getOrigin());
 
diff --git a/shapes/Subtract.cc b/shapes/Subtract.cc
index a2f2d94..dd7a646 100644
--- a/shapes/Subtract.cc
+++ b/shapes/Subtract.cc
@@ -33,6 +33,8 @@ Shape::IntersectionList Subtract::intersect(refptr<Shape> _this, const Ray & ray
 {
     Ray ray_inv = m_inverse.transform_ray(ray);
     IntersectionList res1 = m_shape1->intersect(m_shape1, ray_inv);
+    if (res1.size() == 0)           /* optimization */
+        return res1;
     IntersectionList res2 = m_shape2->intersect(m_shape2, ray_inv);
     BoolIntersectionList merged(res1, res2, ray_inv.getOrigin());